[Ocfs2-devel] [PATCH 37/39] ocfs2: Don't merge in 1st refcount ops of reflink.

[Joel Becker]

On Thu, Apr 30, 2009 at 06:58:49AM +0800, Tao Ma wrote:
> Actually the whole reflink will touch refcount tree 2 times:
> 1. It will add the clusters in the extent record to the tree if it
>    isn't refcounted before.
> 2. It will add 1 refcount to these clusters when it add these
>    extent records to the tree.
> 
> So actually we shouldn't do merge in the 1st operation since the 2nd
> one will soon be called and we may have to split it again. Do a merge
> first and split soon is a waste of time. So we only merge in the 2nd
> round. This is done by adding a new internal __ocfs2_increase_refcount
> and call it with "not-merge" for 1st refcount operation in reflink.
> 
> This also has a side-effect that we don't need to worry too much about
> the metadata allocation in the 2nd round since it will only merge and
> no split will happen for those records.

	Hmm.  My first thought was "eww, awful special case".  But
you're right, the second pass is simpler if we don't have to re-split.
If we crash in between, we may have some could-have-been-merged records,
but the lookup code handles them just fine.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127